This invention relates to a method of manufacturing a black matrix type fluorescent screen of a color picture tube.
For the purpose of improving the contrast of the fluorescent screen of a color picture tube, the so-called black matrix type fluorescent screen is generally used in which spaces between picture elements consisting of phosphors of three colors, that is, green, blue and red are filled or coated with light absorbing substance.
Heretobefore, such a black matrix type fluorescent screen has been manufactured by coating onto the inner surface of the panel of the tube, a slurry prepared by admixing photosensitive liquid consisting of an aqueous solution of polyvinyl alcohol containing ammonium dichromate, with a phosphor and then exposing the coated slurry to light through a shadow mask, thus forming a picture element of a first color. Similar steps are repeated for other colors to prepare picture elements of three colors. Then, a photosensitive solution containing a fine powder of light absorbing substance, graphite for example, is applied onto the three color picture elements and then the coated film is exposed through the panel glass (back exposure) to fill the spaces between the picture elements with the light absorbing substance.
With this method, however, phosphor picture elements are composed of relatively large phosphor particles having a diameter of about 10 microns and moreover, since the picture elements are porous, light transmits through the picture elements at the time of back exposure. For this reason the light absorbing substance remains and fixes on the picture elements. This causes so-called a cross-contamination state, thereby greatly reducing the brightness of reproduced pictures. Furthermore, according to this method, since the phosphor slurry is applied and then exposed to form the picture elements, exposure light would be diffused by the phosphor particles, thus deforming the picture elements, which results in such disadvantages as nonuniformity in white field, and blur of reproduced picture.
Accordingly, at present, a method is widely used in which a black matrix film is firstly formed. With this method, since the particle size of the light absorbing substance is extremely small, the black matrix windows corresponding to the picture elements are sharply defined. Accordingly, it is possible to obtain a fluorescent screen having high quality.
According to this method, however, since it is necessary to remove the photosensitive resin film and the light absorbing substance thereon in order to form black matrix windows, the number of the manufacturing steps increases, thereby reducing productivity.
Incidentally, U.S. Pat. No. 4,273,842 of the same applicant of the present application discloses a fluorescent screen manufacturing method wherein high polymer solution of diazonium salt is coated on the panel inner surface of a tube to form a layer which is rendered sticky when exposed to light, and powder particles such as phosphors are sprayed onto portions of the layer rendered sticky as a result of exposure to complete a fluorescent screen. This method is of a simple dry process and may be applicable to the manufacture of various types of fluorescent screen.